Tube sheet and leakage detection construction for heat exchanger



Sept. 23, 1958 E F. BONl, JR, ETI'AL 2,853,277

TUBE SHEET AND LEAKAGE DETECTION CONSTRUCTION FOR HEAT EXCHANGER FiledApril 16, 1956 ATIURNEYS I K I l l E i l i= 5; 2 35 74 i 25 g 5; 34 I70/ /72 I 0R5 H Fran]! Bani J11, H BY KwrLAGaadner g,

a a u d 75 5 Huh Eon 79 ii Z WEQ 68G v UVA AA United States Patent TUBESHEET AND LEAKAGE DETECTION CON- STRUCTION FOR HEAT EXCHANGER FrankBoni, Jr., Massillon, and Karl A. Gardner and Philip S. Otten, Canton,Ohio, assignors to The Griscom-Russell Company, Massillon, Ohio, acorporation of Delaware Application April 16, 1956, Serial No. 578,436 6Claims. (Cl. 257-231) This invention relates to a tube sheetconstruction for a heat exchanger and more particularly it pertains to aheat exchange tube and tube sheet unit with leakage detection means,adapted for simplified removal and insertion.

Furthermore, the invention relates to a heat exchanger construction ofan interleakproof type for handling fluids whose interleakage could bedisastrous, such as in a steam generator heated by a liquid metal; andmore particularly, the invention relates to a heat exchangerconstruction including double wall tubes for prevention of interleakageof sodium and water together with a measure of accessibility to theinterior of the shell in which the double wall tubes extend fromremovable tube sheet means.

Recently it has been proposed that such heat exchangers should includeportions welded together into an integral shell unit. This has created aproblem in that where an all-welded shell is used with an integral tubesheet, it is difficult if not impossible to determine the soundness,such as by X-ray, of the last weld that closes up the interior of theshell.

Associated with this problem is that of inspecting, cleaning andrepairing parts. This requires periodic access to the interior of theshell and to the heat exchange tubes with a minimum of time and effort.

Moreover, where double-walled tubes are used for detection andprevention of the heat exchange fluids leakage, it is desirable toprovide monitoring means in the tube sheet and communicating with theinterface between the double tubes. Monitoring means usually includes achamber in a tube sheet separated from both of the heat exchange fluids.Such means function satisfactorily in tube sheets that are integral withthe adjacent shell. However, with an all-welded shell it is preferableto use a removable tube sheet in order to gain access to the interior ofthe shell.

Various means may be used to solve certain of these d1fficulties, butthe solution of one problem creates others. For example, if a tube sheetintegral with a shell is replaced with a removable tube and tube sheetarrangement an additional problem of sealing the joint between the tubesheet and the shell arises. This joint may be sealed by welding.However, the weld must be in an accessible position as well asrelatively easy to break when it is desired to remove the tube sheet andtube from the heat exchanger.

Furthermore, other difiiculties are encountered in the apparatus ofprior disclosures. Because of the requirements of accessibility of weldssealing the tube sheet to the barrel wall, it has been diflicult toprovide a passage means between the monitor chamber in the tube sheetand the exterior of the barrel wall. Separate tubes extending betweenthe chamber and the barrel wall across the interface of the tube sheetand barrel wall have proven unsatisfactory. The tube must be severed andreplaced whenever the tube sheet is removed and replaced.

We have discovered that these problems may be over- 2 come by theprovision of a pair of tube sheets secured together in a box-likestructure to provide an enclosed chamber therebetween and to whichdouble-walled tubes' are permanently secured in a fluid-tight manner.The assembly of the tube sheets and the double-walled tubes constitutesa unit which is adapted for ready removal and insertion into a heatexchanger when necessary. To satisfy the problem of detecting andpreventing interleakage of the heat exchange fluids, the outer tubesheet is provided with a peripheral groove alignable with a similargroove in the inner surface of the barrel wall. Spaced welds areprovided in an accessible position for sealing the tube sheet unit tothe barrel wall and enclosing passage means between the tube sheetchamber and the barrel wall.

Generally, it is an object of this invention to provide a box-like tubesheet unit of double tube construction for insertion in the shell of aheat exchanger, whereby separate leakage detection and prevention meansin the barrel wall and tube sheet unit are assembled into a completemonitoring system upon the sealing of the tube sheet unit to the barrelwall.

It is another object of this invention to provide a box-like tube sheetunit of double tube construction for removal from the shell of a heatexchanger, whereby separate leakage detection and prevention means inthe barrel wall and in the tube sheet are disassembled upon breaking thesealed joint between the tube sheet unit and the barrel wall Withoutdisturbing the separate passage means in each of the parts that arejoined when the arrangement is assembled and sealed.

It is another object of this invention to provide a box-like tube sheetunit having double tubes attached thereto for simplified installationand removal from a heat exchanger and having an all welded shell.

It is another object of this invention to provide a tube sheet anddouble tube assembly with a leakage detection and prevention chamberconnected when two spaced welds are made joining and sealing the tubeand tube sheet assembly with the barrel wall.

Finally, it is an object of this invention to provide an improved tubesheet construction with leakage detection means which substantiallyeliminates the difficulties enumerated and which obtains the foregoingdesiderata in a simple and effective manner.

These and other objects and advantages apparent to those skilled in theart from the following description and claims may be obtained, thestated results achieved and described difficulties overcome by thediscoveries, principles, apparatus, parts, combinations, subcombinationsand elements which comprise the present invention, the nature of whichis set forth in the following statement, preferred embodiments ofWhich--illustrative of the best modes in which applicants havecontemplated applying the principles-are set forth in the followingdescription, and which are particularly and distinctly pointed out andset forth in the appended claims forming part hereof.

The nature of the improvements in the tube sheet construction of thepresent invention may be stated in general terms as including in a heatexchanger, connected shell and barrel Walls with inturned shouldermeans, a box-like tube sheet unit seated on the shoulder and includingfirst and second tube sheets forming an enclosed unit chamber, doubletubes Within the shell and having an outer tube secured in one tubesheet and an inner tube secured in the other tube sheet, thetube-to-tube-sheet assembly being removable from the heat exchanger as aunit, the exchanger walls and the tube sheet unit having abuttingfin-like flange means welded together and forming a first barrier forthe joint between the unitv and the exchanger walls, said flange meansforming an annular groove with the exchanger walls and with the tubesheet unit, an annular diaphragm spanning the annular grooves betweenthe tube sheet and the barrel wall and being welded at the inner andouter diaphragm edges to the tube sheet and exchanger wall respectively,the diaphragm being spaced from the welded ends of the flanges, passagerneans communicating between the unit chamber and the annular groove onthe tube sheet unit and passage means extending through the exchangerwall from the annular groove on the exchanger wall to the exterior ofthe exchanger wall.

The preferred embodiments of the invention are illustrated, by way ofexample, in the accompanying drawings wherein:

Fig. l is an elevational view of a heat exchanger involving theimprovements of the invention;

Fig. 2 is an enlarged, fragmentary, vertical sectional view of a portionof the heat exchanger shown in Fig. 1; and

Fig. 3 is a vertical sectional view similar to Fig. 2 showing amodification of the invention.

Similar numerals refer to similar parts throughout various figures ofthe drawings.

In Fig. 1, a heat exchanger is generally indicated at 1. However, it isnot intended that the use of this invention be limited to a specifictype of heat exchanger as the improved construction may be used in manydifferent types of heat exchangers. The heat exchanger 1 includes ashell 2 and a barrel wall 3. The shell 2 and the barrel wall 3 arecomposed of annular portions that are secured together bycircumferential welds including welds 4 and 5 around the shell 2 andwelds 6 and 7 around the barrel wall 3.

A over 8 closes the open end of the barrel wall 3 where it is secured ina conventional manner, such as by a ring of bolts 9. The barrel wall 3includes a fluid inlet 10 and an outlet 11 which are attached by welds12 and 13, respectively. The shell 2 includes a fluid inlet 14 and afluid outlet 15 which are similarly secured by welds 16 and 17,respectively.

As shown in Fig. 2, the heat exchanger 1 includes tube sheet unit,generally indicated at 18 having spaced tube sheet members 19 and 20.The tube sheet unit 18 is a hollow box-like structure. The tube sheets19 and 20 are spaced from each other and provided with circularend-abutting flanges or wall portions 21 and 22, respectively, extendingtoward each other and secured together at their abutting ends by aperipheral weld 23. Thus, the spaced tube sheets 19 and 20 together withthe flanges 21 and 22 form an enclosed chamber 24. The box-like tubesheet unit 18 may be made as shown or in any other way that provides anenclosed chamber between a pair of tube sheets held in spacedrelationship by an annular connecting wall.

In Fig. 2, a double-walled tube, generally indicated at 25, extendsdownwardly from the tube sheets 19 and 20 into the shell 2. Though onedouble-walled tube 25 is shown, it is understood that a plurality ofsuch tubes are used. Each tube 25 includes an inner tube 26 and an outertube 27, both of which tubes are composed of metal and in metal-to-metalor surface-to-surface heat transfer contact with each other. The upperend portions of the tubes 26 and 27 are seated in a fluid-tight manner,such as by expanding within their respective tube sheets 19 and 20.Hence, the inner tube 26 extends through the chamber 24 and between thetube sheets 19 and 20.

The tube sheets 19 and 20 and the tubes 26 and 27 may be assembled in anumber of ways. For example, the outer tube 27 is first inserted andexpanded in a suit able aperture 28 in the tube sheet 20 and weldedthereto at 29, the flanges 21 and 22 are then welded together at 23,inner tube 26 is then inserted into the outer tube 27, the inner tube 26is then expanded in an aperture 30 aligned with the aperture 28 where itis welded a 31, the inner tube 26 is then expanded-preferably in thedirection of the arrow 32 (Fig. 2) with the lower ends of the tubes openin order to obtain surface-to-surface contact within the tubes,thereafter, the lower ends of the tubes 26 and 27 are provided with endcaps 33 and 34, respectively, in a fluid-tight manner.

The double tube 25 is of the bayonet type, as shown in the drawings.However, it is not intended that the present invention be limited to thebayonet type tube; it may be applied to many ditferent types of heatexchange tubes, such as U-tubes. Moreover, the inner tube 26 may bepreferably provided with longitudinal surface grooves such as shown inthe co-pending application of Ernest Bruegger and Philip S. Otten, S. N.380,214, filed September 15, 1953.

The double tube 25 is supported near the lower end by a battle platewhich is connected to the lower end of the tube sheet 20 by a tie rod36. Accordingly, the assembly of the double tube 25, the baffle plate35, and the tie rod 36, constitutes a removable assembly that may bereadily inserted or removed from the heat exchanger 1 as a unit whennecessary for access to the interior of the shell.

As shown in Fig. 2 a circumferential shoulder 37 is provided on theinner surface of the shell 2 which serves as a rest for the tube sheet20. The inner surface of the barrel wall 3 is provided with a groove 38from which a plurality of shear blocks 39 extend and engage the outerperipheral portion of the outer tube sheet 19 and hold the unit 13seated on the shoulder 37. The shear blocks 39 are held in place by aretainer ring 40. Accordingly, the shoulder 37 and the shear blocks 39retain the assembled tube sheets 19 and 20 and tubes 25 againstlongitudinal movement along the vertical axis of the heat exchanger 1.

Within the barrel Wall 3 is a barrel chamber 41 which is divided by athird tube sheet 42 into compartments 43 and 44, the compartment 43being located between the cover 8 and the tube sheet 42 andcommunicating with the fluid inlet 1%, the compartment 44. being locatedbetween the tube sheets 19 and 42 and communicating with the fluidoutlet 11. The tube sheet 42 is mounted on a radial flange 45 on theinner surface of the barrel Wall 3. A plurality of bolts 46 hold thetube sheet 42 against the flange 45. In addition, a spacer plate 47 isattached to the undersurface of the tube sheet 45 by a plurality ofbolts 48. The plate 47 is provided with a plurality of apertures 49, thenumber of which equals the number of double tubes 25 in the heatexchanger 1. Each aperture 49 is aligned with the apertures 223 and 30in the tube sheets 2% and 19, respectively.

In addition, a plurality of tubes 59 are attached to apertured tubesheet 42 and extend downwardly therefrom through the compartment 44-into the inner tube 26, forming an annular space 51 therewith. The upperend of the tube 50 is secured to the upper surface of the tube sheet 42in a fluid-tight manner such as by a weld 52. The tube 50 is encasedwithin an insulation sleeve 53 which extends from the undersurface ofthe spaced plate 47 to the lower end of the tube. Thus, heat exchangefluid entering the inlet 1t (Fig. 1) passes through the compartment 43and moves downwardly through the tube 50 to the lower end of the doubletube 25 where the fluid reverses direction and passes upwardly throughthe annular space 51 and into the lower compartment 44, and thencethrough the outlet 11. At the same time, another fluid enters the inlet14 (Fig. 1), contacts the outer tubes 27 in a heat exchange relationshipand then passes out of the shell 2 through the outlet 15. It is intendedthat either side of the heat exchanger be the hot side. That is, eitherthe fluid passing through the shell or the head maybe the heating fluid.

As shown in Fig. 2, the upper tube sheet 19 is pro vided with peripheralrecess means including a recessed shoulder means 54, a trepan groove 55and a fin-like flange means 56. The shoulder means 54, the trepan groove55 and flange means 56 extend around the periphery of the tube sheet 19.

Likewise, the inner surface of the barrel wall 3 includes a recessedshoulder means 57, a trepan groove 58, and a fin-like flange means 59.The openings for both grooves 55 and 58 face the head chamber 41. Therecessed shoulder 57 is adjacent the groove 38. When the tube sheets 19and 20 are mounted in the heat exchanger, as shown in Fig. 2, the flangemeans 56 and 59 are in surface-to-surface abutment with theircorresponding extremities adjacent each other. In addition, the recessedshoulders 54 and 57 are preferably aligned and receive the edge portionsof an annular diaphragm means 60 that extends between the recessedshoulders. The outer periphery of the diaphragm means 68 is seated inthe recess 57 in a fluid-tight manner by a circumferential weld 61.Likewise, the inner periphery of the diaphragm means 60 is seated in therecess 54 by a circumferential weld 62. Finally, the adjacentextremities of the portions 56 and 58 are secured together in afluid-tight manner such as by an annular weld 63.

Accordingly, a monitoring chamber generally indicated at 68a is providedbetween the tube sheet unit 18 and the barrel wall 3. The monitoringchamber 68a includes the grooves 55 and 58 as well as theinterconnecting space between the diaphragm 6t) and the weld 63. Thechamber 68a is sealed from the heat exchange fluids on either sidethereof.

As shown in Fig. 2, a passage 64 is provided in the upper tube sheet 19extending between the chamber 24 and the groove 55. One or more similarpassages 64 may be provided at spaced intervals around the tube sheet19. In addition, a passage 65 is provided through the barrel wall 3extending radially from the groove 58 to the exterior of the heatexchanger and communicating with a conduit 66, one end of which isconnected to the exterior of the barrel wall 3 by a weld 67.

The foregoing entire construction including the boxlike tube sheet unit18, the double tube 25 and a diaphragm 60 together with the weld 63provides a double barrier between the heat exchange fluids in the heatexchanger l. The box-like tube sheet unit 18 provides a double barrierbetween the heat exchange units inasmuch as the tube sheets 19 and 28are mounted between the head and shell sides of the heat exchanger 1. Inaddition, the double walled tube 25 including inner and outer tubes 26and 27 and the two end plugs 33 and 34 constitutes a double barrierbetween heat exchange fluids circulating through and around the doubletube 25. Finally, the joint between the tube sheet unit 18 and thebarrel wall 3 including the diaphragm 68 and the weld 63 constitutes adouble seal or barrier between the heat exchange fluids.

Moreover, the joints between the inner and outer tubes 26 and 27 andtheir corresponding tube sheets 19 and 28 are sealed by welds 31 and 29,respectively, thereby preventing either fluid from passing through thesejoints. Further, the shell fluid passes between the tube sheet unit 18,and its adjacent parts including the shoulder 37 and the shell 2, aswell as between the fin-like flange means 56 and 59, to the weld 63.Likewise, the head fluid moves into the joints between the shear blocks39, the

foregoing entire construction also provides a monitoring system wherebyeither fluid upon leaking through a failure in one barrier is conveyedultimately into a monitoring system which is provided between all of thedouble barrier elements to prevent interleakage between the fluids. Forexample, one of the heat exchange fluids may leak through one of thejoints between the tubes 26 and 27 and their corresponding tube sheets19 and 20. In such event, the fluid would enter the unit chamber 24 andultimately pass through the passage 64, the chamber 60a, and the passage65 into the conduit 66. Similarly, if one of the welds 61, 62 or 63should develop a leak the leaking fluid would be conducted in a similarmanner to the conduit 66 whereby detection is possible and ultimateinterleakage with the fluid could be prevented. The monitoring systemmay be.operated either in an empty status or with a third fluidcirculated therethrough.

Accordingly, the foregoing construction provides a novel and usefulstructure having three phases; namely, a monitoring system, a doublebarrier between the heat exchange fluids, and removability of theassembled boxlike tube sheet unit and the double tubes.

An alternative form of the invention is shown in Fig. 3 in which meansother than the shear blocks 39 (Fig. 2) is used for locking tube sheetsin position. In Fig. 3 a

barrel wall 68 is provided with a circumferential shoulder' 68a and aseries of spaced lugs or projections 69 extending radially inwardly. .Asimilar series of spaced lugs 70 is provided at a zone longitudinallyspaced from that of the lugs 69. Spaced tube sheets 71 and 72 include acylindrical wall portion 73. Similarly two series of spaced lugs 74 and75, corresponding to lugs 69 and 70, are provided around the tube sheet72 and wall 73. This arrangement of interlocking corresponding lugs isshown in greater detail in Price Patent No. 2,219,659. This type ofjoint locks the unit of tube sheets 71 and 72 seated against theshoulder 68a and against longitudinal movement of the heat exchanger 1.

The spaced tube sheets 71 and 72 and the cylindrical wall portion 73provide a unit chamber 76 similar to the chamber 24. Thus, the tubesheets 71 and 72 together with the wall 73 form a box-like tube sheetunit similar to the unit 18. Moreover, a pair of tubes including outertube 77 and inner tube 78 are assembled with the tube sheets 71 and 72by means of corresponding welds 79 and 80, respectively. Finally, aninlet tube 81 similar to tube 50 is provided having insulation sleeve82.

In Fig. 3, peripheral trepan grooves 83 and 84 are provided in the tubesheet 71 and barrel wall 68, respectively, formed by tin-like flangemeans 85 and 86. The upper extremities of the fin-like flange means 85and 86 are secured together in a fluid-tight manner by an annular weld87. Moreover, a passage 88 communicates between the chamber 76 and thegroove 83, and a passage 89 communicates between the groove 84 and aconduit 90.

A pair of annular grooves 91 and 92 is provided in the inner surface ofthe barrel wall 68 with a radially extending, fin-like flange 93therebetween. Likewise, a trepan groove 94 is provided in the tube sheet71 which with the upper surface of the tube sheet forms a radiallyextending tin-like flange 95 aligned with the flange 93. An annulardiaphragm 96 is mounted between the fin-like flanges and has outer andinner peripheries welded at 97 and 98 to the flanges 93 and 95,respectively.

The unit of the tube sheets 71 and 72 together with the double tubes 77and 78 are assembled by first inserting and expanding the outer tube 77into the apertured tube sheet 72 and welding the same together at 79;then inserting the inner tube 78 into the tube 77; then expanding theinner tube into the surface-to-surface heat exchange relationship withthe outer tube; then expanding the end portion of the inner tube 78 intothe apertured tube sheet 71; and then welding the joint at 80. The lowerends of the tubes 77 and 78 may be provided with end caps similar to endcaps 33 and 34.

The construction of the present invention provides a heat exchanger thatis readily assembled and disassembled and, at the. same time, providesadvantages not present in prior constructions. In operation the heatexchanger may be disassembled in several steps. In Fig. 2, todisassemble the heat exchanger 1 the cover 8 is first removed. The bolts46 are then detached and the tube sheet 42 is lifted out of the headchamber 41 together with the tubes 50 attached thereto. During thisoperation when the lower ends of the tubes 50 reach the upper ends ofthe tubes 26, the bolts 48 are removed from the undersurface of the tubesheet 42 and the spacer plate 47 drops to the lower ends of the tubes 50where it remains during removal of the assembled tube sheet 42 and tubes50. Thus, the plate 47 retains the lower ends 50 in alignment with thepattern of the tubes 26.

Thereafter, the retainer ring 49 is removed and the shear blocks 39 aremoved out of the circumferential. groove 38. The annular diaphragm 60 isthen removed by breaking the welds 61 and 62 after which the weld 63 isbroken. The assembled tubes and box-like tube sheet unit 18 are liftedout of the heat exchanger from the position shown in Fig. 2. Byfollowing the reverse order of the foregoing steps the entire unit maybe reinstalled.

The device of the present invention is an improvement over previousconstructions for several reasons. In the first place, heat exchangersare preferably composed of cylindrical sections welded together inend-to-end abutment. Each weld is examined, such as by X-ray, forsoundness. By providing a removable tube-to-tube-sheet unit the lastweld may be examined for soundness as readily as the previous weldsprior to insertion of the tube and tube sheet assembly.

Moreover, the construction of the present invention provides a doubleseal or barrier including welds between the tube sheet and the barrelwall which are readily accessible from the barrel side of the tube sheetwhen necessary. This, in turn, permits the ready removal of theassembled tube and tube sheet unit without interfering with otherconstructional members. Upon removal of the annular diaphragm 60 bysevering the welds 61, 62 and 63, the assembled tube sheets may belifted vertically from the location shown in Fig. 2.

Furthermore, the construction of the present invention permits theremoval of the tube and tube sheet unit without severing ordisconnecting separate tubes used in the monitoring system. By providingthe diaphragm 60 at a spaced distance from the weld 63 communicationbetween the tube sheet and the barrel head is provided without the useof tubes or pipes of any kind.

Finally, by providing spaced tube sheets 19 and 20 having a spacetherebetween including the flanges or wall portions 21 and 22 anenclosed fluid-tight chamber is provided which is retained intact uponremoval of the tube and tube sheet unit. Upon reinsertion of the unit 18into the heat exchanger communication with the passage 65 through thebarrel wall 3 may be readily restored upon rewelding the fin-likeflanges 56 and 58 and then replacing the annular diaphragm 60 with thewelds 61 and 62.

In the foregoing description certain terms have been used for brevity,clearness and understanding, but no unnecessary limitations are to beimplied therefrom beyond the requirements of the prior art, because suchwords are used for descriptive purposes herein and are intended to bebroadly construed.

Moreover, the embodiments of the improved construction illustrated anddescribed herein are by way of example, and the scope of the presentinvention is not limited to the exact details of construction shown.

Having now described the features, constructions and principles ofinvention, the characteristics of the new heat exchanger tube sheetconstruction with leakage detection means, and the advantageous, new anduseful results provided; the new and useful discoveries, principles,parts, elements, combinations, subcombinations, structures andarrangements, and mechanical equivalents obvious to those skilled in theart, are set forthin the appended claims.

We claim:

1. In a heat exchangeer, integral shell walls forming a shell fluidcontaining chamber, the shell walls having inwardly directed annularshoulder means, head walls forming a head chamber, a box-like tube sheetunit seated on said shoulder separating the shell and head chambers,said unit including two spaced tube sheet members and an annularconnecting wall forming a unit chamber, do 1 .read fluid communicatingwith the head ch nber extending from the unit within the shell walls;said double tubes including telescoped inner and outer tubes in heatexchange contact, each inner tube extending through the unit chamber andbeing seated in a tubereceiving opening formed in one of the tube sheetmembers, and each outer tube being seated in an aligned tubereceivingopening formed in the other tube sheet memher; the shell walls and thetube sheet unit being provided with abutting annular fin-like flangemeans, a welded joint connecting said flange means forming a firstbarrier to head and shell fluid interleakage for the joint between theunit and the shell Walls, diaphragm ring means spaced from the weldedjoint and the flange means welded to the unit and shell walls forming asecond barrier to head and shell fluid interleakage for the jointbetween the unit and exchanger walls, means engaged between the unit andshell walls holding the unit seated on said shoulder, and the assemblyof the tube sheet unit and tubes being separable from the shell wallsupon breaking the first and second barrier welds.

2. The construction set forth in claim 1 in which passage means isformed in the tube sheet unit and in the shell wall communicatingbetween the unit chamber, the space between the first barrier flangemeans and the diaphragm ring means, and the exterior of the shell, whereby monitoring chamber means is provided for the double tubes, the jointsbetween the inner and outer tubes and the spaced tube sheet members, andthe first and second barrier joints.

3. The construction defined in claim 1 in which passage means is formedin the tube sheet unit communicating between the unit chamber and thespace between the first barrier flange means and the diaphragm ringmeans, and in which passage means is formed in the shell wallscommunicating between said space and the exterior of the heat exchanger.

4. The construction defined in claim 1 in which the abutting annularfin-like flange means comprises a first cylindrical fin-like flangemember connected to and extending from the shell walls, said firstflange member being spaced inwardly of the shell walls and formingtherewith a first annular groove, and a second cylindrical finlikeflange member connected to and extending from the unit telescoped Withinthe first flange member, there being a second groove formed between thesecond flange member and an exterior surface of the unit, and in whichthe welded joint forming the first barrier is between the telescopedflange members.

5. The construction defined in claim 4 in which passage means is formedin the tube sheet unit communicating between the unit chamber and thesecond groove, and in which passage means is formed in the shell wallscommunicating with the first groove and the exterior of the heatexchanger.

6. The construction defined in claim 1 in which the diaphragm ring meanscomprises a washer-like metal ring having inner and outer edges, theouter edge of the ring being welded to the shell walls, the inner edgeof the ring being welded to the unit, and in which the ring spans thewelded joint connecting the flange means and forms with the flange meansspaced therefrom an annu lar chamber between the barriers.

(References 011 following page) References Cited in the file of thispatent 2,475,025 UNITED STATES PATENTS 3 312 333 1,948,550 Voorheis Feb.27, 1934 2,187,555 Flindt Jan. 16, 1940 5 2,280,098 Houdry Apr. 21, 1942375,132

10 Hufi July 5, 1949 Lassiat et a1 July 10, 1951 Gardner et a1 Apr. 24,1956 FOREIGN PATENTS Great Britain June 23, 1932

